Image texture not showing, but diffuse does
You need to add a Shader node between the Image Texture and the Mix node - in your case probably a Diffuse Shader - alternatively use a MixRGB Color node to mix the colors before feeding into the existing Diffuse shader. As a general rule you should normally connect sockets to only the same color - in your case you have a yellow (Color) connected to green (Shader) and this is the cause of your problem since green sockets should only ever connect to green (anything else is completely incompatible).

Note that there are some situations where you can mix some node types - eg, the Color of a Texture to a Factor of a Mix node. However, this does result in some conversion between the types which can produce unexpected results. There is no such conversion to or from green sockets.